The invention relates generally to controlling engine overspeeding on a diesel engine, and more specifically to controlling overspeed caused by the ingestion of lubricating oil.
Large self-propelled traction vehicles, such as locomotives, commonly use a diesel engine to drive an electrical generation system comprising generating means for supplying electric current to a plurality of direct current traction motors whose rotors are drivingly coupled through speed-reducing gearing to the respective axle-wheel sets of the vehicle. The generating means typically comprises a main 3-phase traction alternator whose rotor is mechanically coupled to the output shaft of the engine, typically a 16-cylinder turbo-charged diesel engine. When excitation current is supplied to field windings on the rotating rotor, alternating voltages are generated in the 3-phase stator windings of the alternator. These voltages are rectified and applied to the armature windings of the traction motors.
During the xe2x80x9cmotoringxe2x80x9d or propulsion mode of operation, a locomotive diesel engine tends to deliver constant power from the traction alternator to the traction motors, depending on the throttle setting and ambient conditions, regardless of locomotive speed. For maximum performance, the electrical power output of the traction alternator must be suitably controlled so that the locomotive utilizes full engine power. For proper train handling, intermediate power output levels are provided to permit graduation from minimum to full output. But the traction alternator load on the engine must not exceed the power the engine can develop. Overloads can cause premature wear, engine stalling or xe2x80x9cbogging,xe2x80x9d or other undesirable effects. Historically, locomotive control systems have been designed so that the operator can select the desired level of traction power, in discrete steps between zero and maximum, so that the traction alternator, driven by the engine, can supply the power demanded by the traction load and the auxiliary loads.
Engine horsepower is proportional to the product of the angular velocity of the crankshaft and the torque opposing such motion. For the purpose of varying and regulating the engine power, it is common practice to equip a locomotive engine with a speed regulating governor that adjusts the quantity of pressurized diesel fuel (i.e., fuel oil) injected into each of the engine cylinders so that the actual speed (in RPM) of the crankshaft corresponds to a desired speed. The desired speed is set, within permissible limits, by a manually operated lever or handle of a throttle that can be selectively moved in eight steps or xe2x80x9cnotchesxe2x80x9d between a low power position (N1) and a maximum power position (N8). The throttle handle is part of the control console located in the operator""s cab of the locomotive. In addition to the eight conventional power notches, the handle has an xe2x80x9cidlexe2x80x9d position and a continuously variable braking position corresponding to 0-100% of full allowable dynamic braking.
The position of the throttle handle determines the engine speed setting of the associated governor. In a typical electronic fuel injection governor system, the output signal from a controller drives an individual fuel injection pump for each cylinder, allowing the controller to individually control start of fuel injection and duration of fuel injection for each cylinder. The governor compares the desired speed (as commanded by the throttle) with the actual speed of the engine, and it outputs signals to the controller to set fuel injection timing to minimize any deviation therebetween.
The notch call or throttle handle position defines the speed and load on the engine, as requested by the locomotive operator. In response, the main locomotive controller requests the delivery of the required number of volts and amps from the traction alternator to supply the load defined by the notch position. The locomotive controller also transmits a signal representing the speed demand to the electronic fuel injection controller. The electronic fuel injection controller is a speed governor that controls the amount of fuel injected into each engine cylinder to maintain the requested speed. The electronic fuel injection controller is not aware of the load demand by the operator through the setting of the throttle handle. The electronic fuel injection controller calculates the required amount of fuel needed to maintain the desired speed. This fuel quantity is converted to a current pulse duration within the electronic fuel injection controller through a series of look-up tables. The look-up tables map the current duration of fuel injection as a function of engine speed, fuel demand, and start of injection timing. The tables are empirically determined based on bench tests where the fuel delivery quantity is measured while varying engine speed, start of injection timing, and the duration of the current pulse. Obviously, this calibration is determined when the fuel is at a specific temperature and the fuel injection equipment that is essentially new and therefore operating at peak efficiency. Further, the table is generic in that one table is used for all engines in the same engine family. The current pulse as determined from the look-up tables is sent to the pump solenoids that control the injection of fuel into each cylinder. The leading edge of the pulse determine the start of fuel injection, and the pulse duration determines the duration during which fuel is injected into the cylinder.
For each of its eight different speed settings, the engine is capable of developing a corresponding constant amount of horsepower (assuming maximum output torque). When the throttle notch 8 is selected, maximum speed (e.g., 1,050 rpm) and maximum rated gross horsepower (e.g., 4,500) are realized. Under normal conditions, the engine power at each notch equals the power demanded by the electric propulsion system, which is supplied by the engine-driven traction alternator, plus power consumed by certain electrically and mechanically driven auxiliary equipment.
The output power (KVA) of the traction alternator is proportional to the product of the rms magnitude of the generated voltage and load current. The voltage magnitude varies with the rotational speed of the engine, and is also a function of the excitation current magnitude supplied to the alternator field windings. For the purpose of accurately controlling and regulating the amount of power supplied to the electric load circuit, it is common practice to adjust the field strength of the traction alternator to compensate for load changes (traction motor loading and/or auxiliary loading) and minimize the error between actual and desired KVA. The desired power depends on the specific speed setting of the engine. Such excitation control establishes a balanced steady-state condition, resulting in a substantially constant, optimum electrical power output for each position of the throttle handle.
The full load fuel value represents the amount of fuel injected into each cylinder to produce combustion at full engine load. Diesel engines of different sizes have different full load fuel values. Of course, at less than full load, the quantity of fuel injected into each cylinder is lower. In the prior art, mechanically operated fuel injection pumps are controlled by engine rotation for injecting the fuel through a nozzle into the combustion chamber. The pump is manually controllable to avoid injecting excessive fuel values into the cylinder by the position of a set screw, which can be adjusted to decrease or increase the amount of fuel injected, up to a fuel value limit.
Today""s modem diesel engine locomotives may also be equipped with a turbocharger driven by cylinder exhaust for providing compressed air to ignition cylinders. The exhaust gases drive the turbocharger to compress the intake air, which is then ported to the individual engine cylinders. Because the intake air is now compressed, the engine operates at a higher fuel efficiency. The turbocharger shaft is lubricated with engine oil. In one scenario, if the oil seal malfunctions, the lube oil leaks into the turbocharger body and is ingested into the cylinders along with the compressed air. This is not the only means by which lubricating oil may enter the cylinders, as is known in the art. The lubricating oil will ignite in the cylinders just as the fuel ignites. The ignition of the lubricating oil, in addition to the fuel value injected into the cylinder, can cause engine overspeeding, to the point where the engine is rotating at a speed in excess of its design limits. For the most serious cases of oil ingestion, catastrophic damage to the engine and the attached alternator, can occur. Further, since the fuel source is no longer under control, the locomotive operator has no means by which to stop the engine.
The above-mentioned undesirable effects associated with diesel engine overspeed conditions due to lubricating oil ingestion can be mitigated by the present invention, which relates to a novel and unobvious apparatus for controlling the engine during lubrication and oil ingestion by loading the engine main alternator using the dynamic braking grids. That is, the energy from the alternator, as driven by the diesel engine, is dumped into the dynamic brake grids. As a result, the engine slows down, notwithstanding that the amount of fuel provided to each cylinder and the amount of lube oil ingested in each cylinder remains unchanged. Advantageously, this invention is operative in any situation where the engine overspeed; whether due to the ingestion of fuel oil or the injection of excessive quantities of fuel into the cylinders.